1. Field of the Invention
The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device which is configured to suppress EMI.
2. Description of the Related Art
In recent years, liquid crystal display devices have been used as display sections of electric home appliances such as computers and television sets. FIG. 10 is a cross sectional view schematically illustrating a main part of a structure of a typical liquid crystal display device.
As illustrated in FIG. 10, a liquid crystal display panel 2 included in a liquid crystal display device 60 is configured such that (i) a pair of substrates, i.e., a thin film transistor (TFT) array substrate 21 and a color filter (CF) substrate 22, are arranged so as to face each other in parallel at a predetermined distance and (ii) space between the thin film transistor (TFT) array substrate 21 and the color filter (CF) substrate 22 is filled with liquid crystal.
Usually, on the TFT array substrate 21, a plurality of gate wires and a plurality of source wires are arranged, and pixel electrodes are provided in respective regions defined by those wires in a lattice pattern. A common electrode is provided on the almost entire surface of the CF substrate 22. The liquid crystal panel 2 is configured such that, by changing a voltage applied to each of the pixel electrodes and a voltage applied to the common electrode, it is possible to drive the liquid crystal in each pixel and cause an image to be displayed.
Further, the liquid crystal display device 60 includes a backlight unit 3, which is provided on a backside of the liquid crystal display panel 2. The backlight unit 3 is a device which includes a light source such as a fluorescent lamp and which controls properties of light emitted from the light source and backlights the liquid crystal display panel 2. The light emitted from the backlight unit 3 passes through the liquid crystal display panel 2, thereby an image is visibly displayed on a front surface of the liquid crystal display panel 2. Usually, a metal bezel 61 is attached to the liquid crystal display panel 2 so as to cover an upper surface and a side surface of a periphery of the liquid crystal display panel 2.
In the periphery of such a liquid crystal display panel 2, a printed circuit board (PWB: Printed Wire Board or PCB: Printed Circuit Board) 31 is provided, which supplies a predetermined voltage to the gate wires and the source wires provided on the TFT array substrate 21 to thereby drive the liquid crystal. The printed circuit board 31 is electrically connected with the wires provided on the TFT array substrate 21 via a flexible wiring board 30 which has flexibility. Usually, a driver IC 28 is mounted on the flexible wiring board 30.
Among such flexible wiring boards 30, a flexible wiring board on which a driver IC 28 is mounted by COF (Chipon Film) is in wide use because the flexible wiring board does not have a device hole in which the driver IC 28 is to be mounted and therefore can be easily designed such that a pitch of wire patterns is narrow.
As illustrated in FIG. 10, the flexible wiring board 30 is constituted by a film substrate 30a which has flexibility and wire patterns 30b and 30b formed on the film substrate 30a, and the driver IC 28 is mounted by COF and connected to the wire patterns 30b and 30b. Extraction portions 30c and 30d of these wire patterns 30b and 30b are drawn to end portions of the film substrate 30a. The extraction portion 30c is connected to a land part of a source wire 24S of the liquid crystal display panel 2 via an anisotropic conductive film 62. On the other hand, the extraction portion 30d is connected to a wiring land part 31b of a wire pattern 31a on the printed circuit board 31 via an anisotropic conductive film 62, which wiring land part 31b is supplied with an image signal and a voltage based on the image signal.
According to this configuration, by bending the flexible wiring board 30 and providing the printed circuit board 31 in a space between a side surface of the backlight unit 3 and a side wall 61b of the metal bezel 61 as illustrated in FIG. 10, it is possible to reduce the width of an upper wall 61a of the metal bezel 61 which is in a shape of a frame and is attached so as to cover the liquid crystal display panel 2.
FIG. 11 is a plan view illustrating (i) the flexible wiring board 30 which is not bent and (ii) the liquid crystal display panel 2 and the printed circuit board 31 which are connected to each other via the flexible wiring board 30. As illustrated in FIG. 11, usually, a ground pattern 31c is provided on the almost entire surface of the printed circuit board 31 except for circuits such as the wiring land part 31b of the wire pattern 31a. The entire surface of the ground pattern 31c is covered with a solder resist film 31e serving as a corrosion-proof protection film. Note here that the ground pattern 31c has a plurality of ground land parts 31d, each of which is not covered with the solder resist 31e and exposed in a form of a rectangle.
In recent years, with the increased size etc. of a liquid crystal display panel 2, the length of a printed circuit board 31 like above has become greater. This has caused more electromagnetic waves to be generated from the printed circuit board 31. Under the circumstances, an appropriate design to suppress EMI (Electro Magnetic Interface: unnecessary radiation, electromagnetic radiation) is considered important.
An example of such a measure to suppress EMI is as follows. By electrically connecting the ground land parts 31d of the ground pattern 31c of the printed circuit board 31 with the metal bezel 61 at a plurality of points via a strip-shaped electric conductor 63 as illustrated in FIG. 11, it is possible to suppress radiation of electromagnetic waves generated from the printed circuit board 31.
An example of such an electric conductor 63 is one that is constituted by (i) an elastic member 63a such as a sponge and (ii) a metal foil 63b or the like which encloses the elastic member 63a (see FIG. 10). This makes it possible to electrically connect the ground pattern 31c of the printed circuit board 31 with the metal bezel 61 by (i) attaching the electric conductor 63 to the ground land parts 31d of the printed circuit board 31 via a conductive adhesive tape 64 in advance under a condition where the flexible wiring board 30 is not bent as shown in FIG. 11 and then (ii) attaching the metal bezel 61 as shown in FIG. 10 so that the electric conductor 63 is connected to the side wall 61b of the metal bezel 61.
The following Patent Literatures 1 and 2 each describes a liquid crystal display device configured to suppress EMI.
Patent Literature 1 discloses a liquid crystal display device including: a liquid crystal display panel; a frame-shaped metal bezel having a reversed L-shaped cross-section surface made up of an upper wall and a side wall, the frame-shaped metal bezel being attached so as to cover an upper surface and a side surface of a periphery of the liquid crystal display panel; a printed circuit board for driving liquid crystal, the printed circuit board being provided, between the periphery of the liquid crystal display panel and the side wall of the metal bezel, in substantially parallel to and away from the side wall; and an electric conductor in a shape of a plate, the electric conductor electrically connecting the side wall of the metal bezel to a land part of a ground pattern on the printed circuit board, wherein an upper wall of the metal bezel has an insertion hole in which the electric conductor is inserted from outside, one end of the electric conductor inserted in the insertion hole is in contact with both the side wall of the metal bezel and the land part of the ground pattern of the printed circuit board, and the other end of the electric conductor is removably hooked on the insertion hole.
FIG. 8 is a view illustrating a cross section of a liquid crystal display device described in Patent Literature 1. A liquid crystal display device 70 in accordance with FIG. 8 is configured such that (i) an electric conductor 14 in a shape of a plate passes through an insertion hole 13c of a metal bezel 13 and (ii) a ground land part 31d of a printed circuit board 31 is electrically connected to the metal bezel 13 via the electric conductor 14 in the shape of a plate. Since the electric conductor 14 is designed to be removably hooked on the insertion hole 13c, it is possible to easily attach and remove the electric conductor 14 if unnecessary radiation occurs.
According to the liquid crystal display device described in Patent Literature 1, it is possible to attach or remove the electric conductor as appropriate without removing the metal bezel attached so as to cover the liquid crystal display panel, i.e., while keeping the metal bezel attached to the liquid crystal display panel. Therefore, it is possible to easily control a measure to suppress EMI in the liquid crystal display device.
On the other hand, Patent Literature 2 discloses a display device including: a display panel, a frame-shaped metal bezel having a reversed L-shaped cross-section surface made up of an upper wall and a side wall, the frame-shaped metal bezel being attached so as to cover an upper surface and a side surface of a periphery of the display panel; a printed circuit board for driving a panel, the printed circuit board being provided, between the periphery of the display panel and the side wall of the metal bezel, in substantially parallel to and away from the side wall; and an electric conductor in a shape of a strip which electrically connects the side wall of the metal bezel to a land part of a ground pattern on the printed circuit board, wherein the side wall of the metal bezel has a window through which the electric conductor can be seen from outside.
FIG. 9 is a view illustrating a cross section of a liquid crystal display device described in Patent Literature 2. A display device 80 in accordance with FIG. 9 is configured such that (i) a ground land part 31d of a printed circuit board 31 is electrically connected to a metal bezel 13 via an electric conductor 14 and (ii) a window 13c is provided to a side wall 13b of the metal bezel 13 so that displacement of the electric conductor 14 can be easily checked.
According to the liquid crystal display device described in Patent Literature 2, since the side wall of the metal bezel is provided with the window through which the electric conductor provided inside the side wall of the metal bezel can be seen from outside, it is possible to easily check, through the window, whether or not the electric conductor is displaced from an appropriate position while keeping the metal bezel attached to the display panel. As such, it is possible to easily detect displacement of the electric conductor and to efficiently assemble the display device.